Vacuum tube



July 26, 1932. R HARDlNG, JR 1,868,600

VACUUM TUBE Filed May 2, 1928 LNVENTOR ADOBE/Q7 HARD/NG ff?.

A TORNEY Patented July 26, 1932 ROBERT HARDING, JR., OF WHITE PLAINS,

NEW YORK, nssralvonv` To ARGTURUS 'RADIO TUBE COMPANY, NEWARK, NEW A CORPORATION OF'DELAWARE 7 4 VACUUM TUBE Application led May 2,

This invention relates to vacuum tubes and particularly to vacuum tubes adapted to be energized by alternating current. The invention is an improvement over the application of Walter Louis Krahl entitled Vacuum tube construction and circuit therefor, Serial N o. 156,947, filed December 24th 1926.

In operating a thermionic tube with alternating current some difficulty has been experienced in eliminating the hum due to the alternating cycle. There are several reasons why a hum may be produced in the output side of the tube and great care is necessary in designing a tube and circuit therefor to lower' the'hum to a minimum so as not to be objectionable in the radio receiving set. Any

change in the potential of the grid of the tubek is naturally amplied in the plate circuit and hence it is necessary to maintain the grid circuit of the tube as free as possible from changes in potential arisingV from sources outside of the input circuit. In an alternating current thermionic tube it sometimes becomes desirable to have a portion of the grid circuit common with a portion of the heater circuit, and this is particularly true in tubes which have a common connection for the cathode and the heater of the tube permitting the use of a fourterminal base or where the cathode is itself the heater for the tube. In both of these cases there is a drop in potential along the common cathode and heater lead due to the resistance thereof and, therefore along a portion of the grid circuit. This f drop in potential causes a variation of potential on the grid due to the alternating current and the result is a variation in the plate circuit which gives rise to an objectionreas.V serial No. 274,399.y

Other objects of the invention will'y bev apparent as the description thereof proceeds.

The invention has been illustrated in the accompanying drawing which shows a perspective view of a vacuum y'tube embodying the invention with portions of the, tube broken away to more accurately show! the Same.

For purposes of illustration I have showny be heated by a singlefstraight jilament`12 i passing therethrough, both of these Velements being supported from a press 18,'which is 'formed integral with the usual transparent envelope 14 supported upon a base 15v which carries the terminals for making the neces- '12 is supported atits lower end upon a conductor 17 which is sealed in thepress 13 and which is connected by a wire 187toone ofthe heater terminals 16 mounted on the basel'. The upper end of the filament 12 may be supported by a spring wire 19 which is in turn attachedto an upright conductor 20 extend- 'ing' parallel-to the cathode to a point below the same where it is bentinwardly and downwardly tobe sealed in thepress 13. n A glass bead21 is sealed upon the` upright conductor 20 and has sealed into it two supports 22 and 23 for rigidly supporting respectively the 'upsary Aconnections `to thek tube. Thejiilament per end of theplate 24 which surroundsV the 'y Vcathode 11 and the upper end of the grid 25 which is interposed betweenthe cathodeand theplate. The lower end of boththe platek 'and grid are supported respectively by means of one Vor more conductors 26 and 27 sealed in the press. One of these conductors 26 from 'theplate is connected' by means of. a wire 28 to the plate terminal 29 at the base ofthe tube, whileone of the supports27 for the .lower end of the grid is connectedbymeans of awire 30 tothe gridterminal 3l'on the base.v VThe lower end of the cathode 11 .A

n.may be rigidly attachedto a conductor-32 ywhich is sealed inthe press-,13fand connected by means lof apseparate wire 33 to the other Y ffilamentfterminal 34. The upper end ofthe cathode@r 11A may beV rigidly supported by means of a strip upon an auxiliary upminals, said cathode extending beyond both right 3G which is sealed in the glass bead 31 extremities of said anode and control elecand therefore insulated from the other eletrode.

ments. The conductor 30 which is electrically connected to the upper end of the filament 12 is connected by means of the wire 37 to the filament terminal 34e.

The lament terminals 16 and 34 may be connected to the secondary 38 of a transformer 39 the primary l() of which may be connected across a source of alternating current 4 as shown.

It will be noted that the cathode extends beyond the plate and grid at both ends so as to form an elfective shield between them and the filament to eliminate hum which might otherwise arise from the direct emission of the lament to the grid and plate.

y It will be evident from the above description that the upper and lower ends of the lfilament 12 are connected respectively to terminals 34 and 16 on the base 15 and that the connection to the cathode 11 is made by the wire 33 entirely separately from the filament circuit, down to the filament terminal 34 at the base of the tube. Inasmuch as the terminals on the base of the tube are made of a conducting material having low resistance, there is practically no potential drop in the terminal itself due to the alternating current passing through the terminal, and if the grid return lead 42 of the circuit is connected directly to the corresponding terminal on the socket into which the tube fits, the drop in potential in this circuit will be so small as to be absolutely negligible so that substantially no efect is produced on the grid of the tube.

It will be seen, therefore, that I have provided a means to absolutely eliminate hum arising through an alternating potential drop in the grid circuit of a tube provided with four terminals to lit into a standard four terininal socket and which is not dependent on the current used to energize the heater.

While I have shown the invention in connection with a heater type tube of a certain specific construction, it is apparent that the invention is applicable to any heater type tube. I do not, therefore, desire to limit myself to the speciic construction described but to interpret the invention broadly within the scope of the appended claim.

`What I claim is:

In a vacuum tube, an envelope, a cylindrical cathode within said envelope, a single straight lament within said cylindrical cathode,- anode and control electrode elements within said envelope, a base on said envelope, a terminal on said base, a connection between said terminal and one end of said filament, a second terminal on said base, a connection between said second terminal and the other end of said lament, and a separate connection between said cathode and one of said ter- In testimony whereof, I ailiX my si nature.

ROBERT HARDIN JR. 

